One example of this type of magnetic memory device is the magnetic memory device disclosed by the present applicant in Japanese Laid-Open Patent Publication No. 2004-178623. This magnetic memory device is a magnetic random access memory (MRAM) and is constructed by laying out a plurality of storage cells, which are each equipped with a pair of magnetoresistive effect elements and a pair of backflow preventing diodes, in two dimensions. Binary information is stored in each storage cell by setting the resistance of one of the magnetoresistive effect elements higher than the resistance of the other magnetoresistive effect element.
With this magnetic memory device, when the information stored in one out of the plurality of storage cells is read out, a pair of transistors (column selecting transistors) are driven via a Y-direction address decoder shown in FIG. 9 of the publication so that current can be supplied via current/voltage converting resistors to a pair of sense bit lines (current supplying lines) that are connected to the respective emitter terminals of the column selecting transistors. Also, by driving one constant current circuit via an X-direction address decoder, it is possible to produce a state where a constant current can be drawn from the storage cells connected to one sense word line (a current drawing line) connected to the constant current circuit. By doing so, the storage cell that is disposed at an intersection of the pair of current supplying lines and the current drawing line and is connected to both types of lines is selected, and currents in proportion to the resistances of the respective magnetoresistive effect elements respectively flow in a first circuit from a power supply to ground via one of the current/voltage converting resistors, one of the column selecting transistors, one of the magnetoresistive effect elements included in the selected storage cell, one of the backflow preventing diodes, and a constant current circuit and in a second circuit from the power supply to ground via the other current/voltage converting resistor, the other column selecting transistor, the other magnetoresistive effect element included in the selected storage cell, the other backflow preventing diode, and the constant current circuit. Voltages that are proportionate to the currents flowing in the respective circuits are generated across both ends of the respective current/voltage converting resistors disposed in the circuits. Accordingly, by detecting the voltages generated across the respective current/voltage converting resistors (or the difference between such voltages), it is possible to detect the relative magnitudes of the resistances of the magnetoresistive effect elements included in the selected cell and to thereby read the information stored in such storage cell.
Patent Document 1
Japanese Laid-Open Patent Publication No. 2004-178623